Data communication networks may include various computers, servers, nodes, routers, switches, hubs, proxies, and other devices coupled to and configured to pass data to one another. These devices are referred to herein as “network elements,” and may provide a variety of network resources on a network. Data is communicated through data communication networks by passing protocol data units (such as packets, cells, frames, or segments) between the network elements over communication links on the network. A particular protocol data unit may be handled by multiple network elements and cross multiple communication links as it travels between its source and its destination over the network. Hosts such as computers, telephones, cellular telephones, Personal Digital Assistants, tablets and other types of consumer electronics connect to and transmit/receive data over the communication network and, hence, are users of the communication services offered by the communication network.
Network elements (e.g. Access Points, Mobility Switches and Edge Switches) are typically implemented to have a control plane that controls operation of the network element and a data plane that handles traffic flowing through the network. The data plane typically will have a collection of line cards having ports that connect to links on the network. Data is received at a particular port, switched within the data plane, and output at one or more other ports onto other links on the network. The packets are transferred across the network in accordance with a particular protocol, such as the Internet Protocol (IP).
Ports can fail for many reasons, including line card failure, failure of the link connected to the port (e.g. line cut), far-end line card failure, etc. Likewise, the internal forwarding datapath within the network element may fail which may cause a port or set of ports to appear to have failed, or there may be some other failures along the logical/virtual connection to the port's external peer endpoint. There are numerous reasons why a port may fail.
In the event a port fails, traffic flowing through the port should be diverted to flow out an alternate port to enable connectivity to be restored through the network. To minimize impact on the traffic being handled by the network element, e.g. to minimize downtime and packet loss, the quicker the rerouting of traffic can occur the better.
Over time, the manner in which network elements handle data has evolved. For example, two or more physical links may extend between a group of network elements and be used collectively as a multi-link trunk (MLT). When the links of an MLT are physically connected to two different network elements, the MLT is referred to as a Split Multi-Link Trunk (SMLT). In particular, each of the links in the MLT may be used by either of the network elements to forward data to the other. Thus, if a first network element has data (e.g., a frame/packet) to send to a second network element, the first network element may select one of the links from the MLT and transmit the packet over that link to the second network element.
As noted above, depending on the manner in which the network elements are interconnected, there may be many ways for the network element to forward a frame/packet to enable the frame/packet to reach its destination. As used herein, the term “cluster” is used to refer to one or more nodes providing node-level resiliency at the network level. Logical connections between the cluster nodes are referred to herein as Inter-Switch Trunks (ISTs). ISTs may be physical links that extend from one network element to a neighboring network element in the cluster, or may be logical links that tunnel through one or more intermediate network elements within the cluster. The node that receives a packet will be referred to as a local node. All other nodes within the cluster are referred to as remote nodes with respect to the received packet.
When a logical port is implemented as a MLT or SMLT, there are actually multiple physical ports that are capable of forwarding a packet to its next hop on the network. Accordingly, if one of the ports of a MLT/SMLT fails, it would be advantageous to cause the packet to be forwarded on one of the remaining ports so that the packet can traverse the network rather than being dropped
In order to achieve low operation cost and easy maintenance, virtualization technology has been widely used in modern communication network. With the help of virtualization and the technologies built on top of it, such as Multi Protocol Label Switching (MPLS), Virtual Private Network (VPN) Lite, and Provider Link State Bridging (PLSB), multiple users can share a common core network without interfering with each other. All these technologies allow users to extend their private network across shared common core network or layer 3 network. For such users, providing network redundancy and high availability to remote network nodes across a layer 3 network becomes a crucial requirement.